Solid-state imaging apparatus and method for producing the same

ABSTRACT

A solid-state imaging apparatus includes a plurality of photosensitive cells, and a driving unit provided for driving the plurality of photosensitive cells. Each photosensitive cell includes a photodiode formed to be exposed on a surface of a semiconductor substrate for the purpose of accumulating signal charge obtained by subjecting incident light to photoelectric conversion, a transfer transistor for transferring signal charge accumulated by the photodiode, a floating diffusion layer for temporarily accumulating signal charge transferred by the transfer transistor, and an amplifier transistor for amplifying signal charge temporarily accumulated in the floating diffusion layer. A source/drain diffusion layer provided in the amplifier transistor is covered with a salicide layer, and the floating diffusion layer is formed to be exposed on a surface of the semiconductor substrate.

This application is a continuation of application U.S. Ser. No.11/726,437, filed Mar. 22, 2007, which is a division of U.S. Ser. No.10/809,215, filed Mar. 25, 2004, which application is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging apparatusequipped with an area image sensor used for a household video camera, adigital still camera, a camera for a mobile telephone, etc., and amethod for producing the solid-state imaging apparatus.

2. Description of the Related Art

FIG. 13 is a circuit diagram showing a configuration of a conventionalsolid-state imaging apparatus 90. Photosensitive cells 98 composed ofphotodiodes 95, transfer gates 96, amplifier transistors 92, and resettransistors 97 are arranged in a matrix (3 row×3 column).

Drains of the amplifier transistor 92 and the reset transistor 97 areconnected to a common drain line 306. A source of the amplifiertransistor 92 is connected to a vertical signal line 15, as shown inFIG. 13. One end of the vertical signal line 15 is connected to a loadtransistor 305, and the other end thereof is connected to a noisesuppressing circuit 12. Outputs of the noise suppressing circuit 12 areconnected to horizontal transistors 14 driven by a horizontal drivercircuit 13. Each photosensitive cell 98 is driven by a vertical drivercircuit 11.

FIG. 14 is plan view showing a configuration of the photosensitive cells98 provided in the conventional solid-state imaging apparatus 90. Asignal of the photodiode 95 is read to a floating diffusion layer 91through the transfer gate 96. The signal that has been subjected tovoltage conversion in the floating diffusion layer 91 is applied from afloating diffusion layer contact 203 to a gate 304 of the amplifiertransistor 92. A source/drain of the amplifier transistor 92 isconnected to the common drain line 306 and the vertical signal line 15.A signal charge in the floating diffusion layer 91 is discharged to thecommon drain line 306 through the reset transistor 97.

FIG. 15 is a cross-sectional view along a plane XYZW shown in FIG. 14.The photodiode 95 composed of an n-type photodiode diffusion layer 402and a p-type leakage blocking layer 403 is formed in a P-typesemiconductor substrate 9.

A gate electrode of a MOS transistor constituting the transfer gate 96,the reset transistor 97, and the amplifier transistor 92 has adouble-layered structure of a polysilicon layer 406 and a salicide layer407.

The floating diffusion layer 91 has the salicide layer 407 on a doublediffusion layer composed of an LDD diffusion layer 404 and asource/drain diffusion layer 405.

A source/drain of the MOS transistor has the salicide layer 407 on thedouble diffusion layer composed of the LDD diffusion layer 404 and thesource/drain diffusion layer 405. The salicide layer 407 does nottransmit light, so that it is removed from an upper portion of thephotodiode 95.

FIGS. 16 to 19 are cross-sectional views showing a method for producingthe conventional solid-state imaging apparatus 90. As shown in FIG. 16,after a device separating layer 502 is formed on a semiconductorsubstrate 9, a resist 501 is formed in a predetermined pattern byphotoetching, and an n-type photodiode diffusion layer 402 and a p-typeleakage blocking layer 403 are formed by ion implanting.

After the resist 501 is removed, a polysilicon layer 406 to be gateelectrodes of MOS transistors constituting the transfer gate 96, thereset transistor 97, and the amplifier transistor 92 is formed, as shownin FIG. 17. Thereafter, a salicide blocking film 503 is formed so as tocover the photodiode 95, and then, a LDD diffusion layer 404 is formedso as to be self-aligned with the polysilicon layer 406 by ionimplanting.

Then, as shown in FIG. 18, an LDD oxide film 504 is deposited so as tocover the salicide blocking film 503, the polysilicon film 406, and theLDD diffusion layer 404. Then, as shown in FIG. 19, the LDD oxide film504 is removed by anisotropic etching, whereby parts of the LDD oxidefilm 504 remain on both sides of the polysilicon layer 406 depositedthick in a vertical direction. A source/drain diffusion layer 405 isformed so as to be self-aligned with the LDD oxide film 504. Thereafter,metal materials such as titanium (Ti), cobalt (Co), etc. are depositedby sputtering, followed by heating. As a result, only the portions wherethe semiconductor substrate and polysilicon are exposed are salicided,and a salicide layer 407 remains.

In the above-mentioned configuration of the photosensitive cells in theconventional solid-state imaging apparatus, the floating diffusion layer91 temporarily accumulates a signal of the photodiode 95. At this time,when there is a pn-junction opposite-direction leakage current in thefloating diffusion layer 91, the leakage current is superimposed on thesignal to generate noise.

The time for signal charge to remain is shorter than that for thephotodiode 95 to subject incident light to photoelectric exchange andstore it. Therefore, a requirement for a pn-junction opposite-directionleakage current is not so strict as in a photodiode; however, when thefloating diffusion layer 91 is produced in the same way as insource/drain of other transistors, a pn-junction opposite-directionleakage current is increased and causes serious noise. When this noiseis large, the sensitivity of the solid-state imaging apparatus isdecreased to degrade an S/N ratio of a signal, etc.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to provide a solid-state imaging apparatus having small noiseand high sensitivity, and a method for producing the same.

A solid-state imaging apparatus according to the present inventionincludes a plurality of photosensitive cells disposed in a matrix in aphotosensitive region on a semiconductor substrate, and a driving unitfor driving the plurality of photosensitive cells. Each of thephotosensitive cells includes a photodiode formed to be exposed on asurface of the semiconductor substrate, for accumulating signal chargeobtained by subjecting incident light to photoelectric exchange, atransfer transistor formed on the semiconductor substrate fortransferring the signal charge accumulated in the photodiode, a floatingdiffusion layer formed on the semiconductor substrate for temporarilyaccumulating the signal charge transferred by the transfer transistor,and an amplifier transistor formed on the semiconductor substrate, foramplifying the signal charge temporarily accumulated in the floatingdiffusion layer. A source/drain diffusion layer provided in theamplifier transistor is covered with a salicide layer, and the floatingdiffusion layer is formed to be exposed on the surface of thesemiconductor substrate.

A method for producing the above-mentioned solid-state imaging apparatusaccording to the present invention includes forming the photodiode, thetransfer transistor, and the amplifier transistor on the semiconductorsubstrate, forming a resist in a predetermined pattern so as to coverthe photodiode, the transfer transistor, and the amplifier transistor,implanting ions into the semiconductor substrate using the resist as amask so as to form the floating diffusion layer, removing the resist andforming a salicide blocking film so as to cover the floating diffusionlayer and the photodiode, forming a source/drain diffusion layer of theamplifier-transistor, and forming a salicide layer so as to cover thesource/drain diffusion layer of the amplifier transistor.

Another method for producing the above-mentioned solid-state imagingapparatus according to the present invention includes forming a resistin a predetermined pattern on the semiconductor substrate, implantingions using the resist as a mask so as to form the photodiode, removingthe resist and forming the transfer transistor and the amplifiertransistor on the semiconductor substrate, forming a first salicideblocking film so as to cover the photodiode, implanting ions into thesemiconductor substrate so as to form the floating diffusion layer andthe source/drain diffusion layer of the amplifier transistor, forming asecond salicide blocking film so as to cover the floating diffusionlayer, and forming a salicide layer so as to cover the source/draindiffusion layer of the amplifier transistor.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a configuration of a solid-stateimaging apparatus according to the present embodiment.

FIG. 2 is a plan view showing a configuration of main portions of thesolid-state imaging apparatus according to the present embodiment.

FIG. 3 is a cross-sectional view showing a method for producing asolid-state imaging apparatus according to the present embodiment.

FIG. 4 is a cross-sectional view showing the method for producing asolid-state imaging apparatus according to the present embodiment.

FIG. 5 is a cross-sectional view showing the method for producing asolid-state imaging apparatus according to the present embodiment.

FIG. 6 is a graph showing the frequency of a conjunction leakage currentin the solid-state imaging apparatus according to the presentembodiment.

FIG. 7 is a graph showing a relationship between an impurityconcentration of a floating diffusion layer and a conjunction leakagecurrent in the solid-state imaging apparatus according to the presentembodiment.

FIG. 8 is a cross-sectional view showing another method for producing asolid-state imaging apparatus according to the present embodiment.

FIG. 9 is a cross-sectional view showing another method for producing asolid-state imaging apparatus according to the present embodiment.

FIG. 10 is a cross-sectional view showing another method for producing asolid-state imaging apparatus according to the present embodiment.

FIG. 11 is a plan view showing a configuration of main portions ofanother solid-state imaging apparatus according to the presentembodiment.

FIG. 12 is a circuit diagram showing a configuration of a dynamic logiccircuit provided in the solid-state imaging apparatus according to thepresent embodiment.

FIG. 13 is a circuit diagram showing a configuration of a conventionalsolid-state imaging apparatus.

FIG. 14 is a plan view showing a configuration of main portions of theconventional solid-state imaging apparatus.

FIG. 15 is a cross-sectional view showing a configuration of theconventional solid-state imaging apparatus.

FIG. 16 is a cross-sectional view showing a conventional method forproducing a solid-state imaging apparatus.

FIG. 17 is a cross-sectional view showing the conventional method forproducing a solid-state imaging apparatus.

FIG. 18 is a cross-sectional view showing the conventional method forproducing a solid-state imaging apparatus.

FIG. 19 is a cross-sectional view showing the conventional method forproducing a solid-state imaging apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the solid-state imaging apparatus according to the presentembodiment, the source/drain diffusion layer provided in the amplifiertransistor is covered with a salicide layer, and the floating diffusionlayer is formed so as to be exposed on a surface of the semiconductorsubstrate. Therefore, the salicide layer is not formed on the surface ofthe floating diffusion layer. Thus, a pn-junction opposite-directionleakage current is reduced in the floating diffusion layer. As a result,a solid-state imaging apparatus with small noise and high sensitivitycan be obtained.

In the present embodiment, it is preferable that an impurityconcentration of the floating diffusion layer is lower than an impurityconcentration of the source/drain diffusion layer of the amplifiertransistor.

It is preferable that each of the photosensitive cells further includesa reset transistor for resetting the floating diffusion layer. It alsois preferable that the driving unit includes a vertical driver circuitfor simultaneously driving the transfer transistor and the resettransistor in a vertical direction, a noise suppressing circuit forobtaining a signal output to a plurality of vertical signal linesdisposed in a vertical direction in the photosensitive region, and ahorizontal driver circuit for outputting a signal from the noisesuppressing circuit in a time series by successively switching aplurality of horizontal transistors disposed in a horizontal direction.It also is preferable that an impurity concentration of the floatingdiffusion layer is lower than an impurity concentration of asource/drain diffusion layer provided in a plurality of transistorsconstituting the vertical driver circuit and the horizontal drivercircuit.

It is preferable that the source/drain diffusion layer provided in theplurality of transistors constituting the vertical driver circuit andthe horizontal driver circuit is covered with a salicide layer.

It is preferable that the transfer transistor and the amplifiertransistor are composed of an n-type MOS transistor.

It is preferable that the vertical driver circuit and the horizontaldriver circuit are composed of a dynamic logic circuit.

It is preferable that an impurity concentration of a source/draindiffusion layer of a part of the plurality of transistors constitutingthe vertical driver circuit and the horizontal driver circuit is lowerthan an impurity concentration of a source/drain diffusion layer ofanother part of the plurality of transistors constituting the verticaldriver circuit and the horizontal driver circuit.

It is preferable that a source/drain diffusion layer of a part of theplurality of transistors constituting the vertical driver circuit andthe horizontal driver circuit is formed to be exposed on a surface ofthe semiconductor substrate, and a source/drain diffusion layer ofanother part of the plurality of transistors constituting the verticaldriver circuit and the horizontal driver circuit is covered with asalicide layer.

It is preferable that an impurity concentration of the floatingdiffusion layer is 1×10¹⁸ cm⁻³ or less.

A method for producing the solid-state imaging apparatus according tothe present embodiment includes forming a salicide blocking film so asto cover a floating diffusion layer and a photodiode, forming asource/drain diffusion layer of an amplifier transistor, and forming asalicide layer so as to cover the source/drain diffusion layer of theamplifier transistor. Therefore, the salicide layer is not formed on thesurface of the floating diffusion layer. Thus, in the floating diffusionlayer, a pn-junction opposite-direction leakage current is reduced. As aresult, a solid-state imaging apparatus with small noise and highsensitivity can be obtained.

It is preferable that an impurity concentration of the floatingdiffusion layer is lower than an impurity concentration of thesource/drain diffusion layer of the amplifier transistor.

A method for producing the solid-state imaging apparatus according toanother embodiment includes forming a second salicide blocking film soas to cover a floating diffusion layer, and forming a salicide layer soas to cover a source/drain diffusion layer of an amplifier transistor.Therefore, the salicide layer is not formed on the surface of thefloating diffusion layer. Thus, in the floating diffusion layer, apn-junction opposite-direction leakage current is reduced. As a result,a solid-state imaging apparatus with small noise and high sensitivitycan be obtained.

Hereinafter, the present invention will be described by way ofillustrative embodiments with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of a solid-stateimaging apparatus 100 according to the present embodiment.Photosensitive cells 8 composed of photodiodes 5, transfer gates 6,amplifier transistors 2, and reset transistors 7 are arranged in amatrix (3 row×3 column).

Drains of the amplifier transistor 2 and the reset transistor 7 areconnected to a common drain line 306. A source of the amplifiertransistor 2 is connected to a vertical signal line 15, as shown inFIG. 1. One end of the vertical signal line 15 is connected to a loadtransistor 305, and the other end thereof is connected to a noisesuppressing circuit 12. Outputs of the noise suppressing circuit 12 areconnected to horizontal transistors 14 driven by a horizontal drivercircuit 13. Each photosensitive cell 8 is driven by a vertical drivercircuit 11.

FIG. 2 is plan view showing a configuration of the photosensitive cells8 provided in the solid-state imaging apparatus 100. A signal of thephotodiode 5 is read to a floating diffusion layer 1 through thetransfer gate 6. The signal that has been subjected to voltageconversion in the floating diffusion layer 1 is applied from a floatingdiffusion layer contact 203 to a gate 304 of the amplifier transistor 2.A source/drain of the amplifier transistor 2 is connected to the commondrain line 306 and the vertical signal line 15. Signal charge in thefloating diffusion layer 1 is discharged to the common drain line 306through the reset transistor 7.

FIGS. 3 to 5 are cross-sectional views showing a method for producingthe solid-state imaging apparatus 100 according to the presentembodiment. Referring to FIG. 3, a polysilicon layer 406 to be gateelectrodes of MOS transistors constituting the transfer gate 6, thereset transistor 7, and the amplifier transistor 2 is formed.Thereafter, a resist 701 formed so as to open a portion to be a floatingdiffusion layer by photoetching is formed. Then, a low-concentrationfloating diffusion layer 1 is formed by ion implantation, using theresist 701 as a mask.

Thereafter, as shown in FIG. 4, a salicide blocking film 503 is formedso as to cover the photodiode 5 and the floating diffusion layer 1.

Then, as shown in FIG. 5, a source/drain layer 3 and a salicide layer 4are formed by the same method as that of the above-mentioned prior art.

FIG. 6 is a graph showing the frequency of a conjunction leakage currentin the solid-state imaging apparatus 100. A horizontal axis representsthe magnitude of a conjunction leakage current, and a vertical axisrepresents the number of pn-junction floating diffusion layersrepresenting the junction leakage current of the horizontal axis. Asolid line 601 represents a distribution regarding the case where thesalicide layer 4 is formed on the floating diffusion layer 1, and adotted line 602 represents a distribution regarding the case where thesalicide layer 4 is not formed on the floating diffusion layer 1.Compared with the case where the salicide layer 4 is not formed on thefloating diffusion layer 4, the entire distribution is shifted to alarger conjunction leakage current in the case where the salicide layer4 is formed on the floating diffusion layer 4. Furthermore, there is adistribution 603 in which a conjunction leakage current locally is verylarge. This leads to a point defect, resulting in a defectivesolid-state imaging apparatus.

FIG. 7 is a graph showing a relationship between the impurityconcentration and the conjunction leakage current of the floatingdiffusion layer 1 in the solid-state imaging apparatus 100. A horizontalaxis represents the impurity concentration of the floating diffusionlayer 1, and a vertical axis represents a conjunction leakage current.When the impurity concentration of the floating diffusion layer 1reaches 1×10¹⁸ cm⁻³ or more, a conjunction leakage current is increasedrapidly.

As described above, according to the present embodiment, thesource/drain diffusion layer 3 provided in the amplifier transistor 2 iscovered with the salicide layer 4, and the floating diffusion layer 1 isformed so as to be exposed on the surface of the semiconductor substrate9. Therefore, the salicide layer 4 is not formed on the surface of thefloating diffusion layer 1. Thus, a pn-junction opposite-directionleakage current is reduced in the floating diffusion layer 1. As aresult, a solid-state imaging apparatus with small noise and highsensitivity can be obtained.

FIGS. 8 to 10 are cross-sectional views showing another method forproducing a solid-state imaging apparatus according to the presentembodiment. The same components as those described with reference toFIGS. 3 to 5 are denoted with the same reference numerals as thosetherein. Thus, the detailed description of these components will beomitted here.

Referring to FIG. 8, an LDD diffusion layer is formed in the same way asin FIGS. 4 and 5 as described above. Referring to FIG. 9, a secondsalicide blocking film 801 is formed so as to cover a floating diffusionlayer 1. Thereafter, as shown in FIG. 10, a source/drain layer 3 and asalicide layer 4 are formed in the same way as in the above prior art.

FIG. 11 is a plan view showing a configuration of main portions ofanother solid-state imaging apparatus according to the presentembodiment. The same components as those described with reference toFIG. 2 are denoted with the same reference numerals as those therein.Thus, the detailed description of the components will be omitted here.

In the floating diffusion layer 1, instead of decreasing the impurityconcentration of a diffusion layer by removing a salicide layer over anentire region, the salicide layer may be removed in a partial region todecrease the impurity concentration of the diffusion layer. In FIG. 11,it is effective to decrease the concentration by removing the salicidelayer in a region other than a periphery 901 of a contact portion 203 ofthe floating diffusion layer 1.

FIG. 12 is a circuit diagram showing a configuration of a dynamic logiccircuit provided in the solid-state imaging apparatus according to thepresent embodiment. Recently, a CMOS logic has become mainstream of asemiconductor. Therefore, a MOS-type imaging apparatus often isconfigured using a CMOS logic. According to the CMOS logic, the stepsare long and determined in view of miniaturization of a transistor, sothat it is very difficult to change the steps due to a sensor.

Particularly, in the miniaturized steps, a p-channel transistor isdifficult to form. The reason for this is as follows: the mass of boron,which is a p-type impurity, is relatively low and the atoms are likelyto move, so that it is difficult to produce a miniaturized transistorusing boron. Therefore, in order to perform production steps peculiar toa sensor, using a miniaturized transistor, it is advantageous toconfigure a transistor only with a NMOS.

When a circuit only with an NMOS is used, power consumption generally isincreased compared with the case using a CMOS. Therefore, a dynamiclogic circuit is used. The dynamic logic circuit performs an operationcalled booting for raising a voltage by the capacitance of a MOS. When aleakage current is increased, the MOS capacitance portion is notoperated, either. This is exactly matched with the object of the presentinvention of decreasing a leakage current.

Particularly, in an imaging apparatus applied to a digital still camera,there is a mode (long-duration exposure) for a very slow operation.Therefore, even in the NMOS dynamic logic circuit, it is necessary toperform isolation of a low leakage current. FIG. 12 shows an example ofa shift register circuit configured using a dynamic circuit. Thedescription of the operation will be omitted here. When a leakagecurrent of the MOS capacitance 902 is large, a slow operation cannot beperformed. It is very effective to use isolation of the presentinvention for isolation of the MOS capacitance 902.

More specifically, when the solid-state imaging apparatus isminiaturized, in establishing a low leakage current technique intendedto provide higher performance such as isolation, p-ch that makes itdifficult to produce a miniaturized transistor is excluded to configurea transistor only with an N-chMOS, and to design a dynamic logic circuitfor lower power consumption as in a CMOS, it is necessary to decrease aleakage current. A miniaturized transistor, a MOS only with n-channels,low leakage isolation, and a dynamic logic circuit are the shortestroute for realizing a solid-state imaging apparatus with highperformance.

As described above, according to the present embodiment, a solid-stateimaging apparatus with small noise and high sensitivity and a method forproducing the same can be provided.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A solid-state imaging apparatus, comprising: a plurality ofphotosensitive cells disposed in a matrix in a photosensitive region ona semiconductor substrate; and a driving unit for driving the pluralityof photosensitive cells, wherein an impurity concentration of asource/drain diffusion layer of a transistor in the photosensitive cellsis lower than an impurity concentration of the source/drain diffusionlayer of a transistor in the driving unit.
 2. The solid-state imagingapparatus according to claim 1, wherein each of the photosensitive cellsincludes: a photodiode formed to be exposed on a surface of thesemiconductor substrate, for accumulating signal charge obtained bysubjecting incident light to photoelectric exchange; a transfertransistor formed on the semiconductor substrate, for transferring thesignal charge accumulated in the photodiode; a floating diffusion layerformed on the semiconductor substrate, for temporarily accumulating thesignal charge transferred by the transfer transistor, the floatingdiffusion layer including a contact portion that is connected to a gateelectrode of an amplifier transistor; and the amplifier transistor beingformed on the semiconductor substrate, for amplifying the signal chargetemporarily accumulated in the floating diffusion layer, wherein animpurity concentration of the floating diffusion layer is lower than animpurity concentration of the source/drain diffusion layer of atransistor in the driving unit.
 3. The solid-state imaging apparatusaccording to claim 2, wherein the impurity concentration of the floatingdiffusion layer is 1×10¹⁸ cm⁻³ or less.
 4. The solid-state imagingapparatus according to claim 1, wherein each of the photosensitive cellsincludes: a photodiode formed to be exposed on a surface of thesemiconductor substrate, for accumulating signal charge obtained bysubjecting incident light to photoelectric exchange; a transfertransistor formed on the semiconductor substrate, for transferring thesignal charge accumulated in the photodiode; a floating diffusion layerformed on the semiconductor substrate, for temporarily accumulating thesignal charge transferred by the transfer transistor, the floatingdiffusion layer including a contact portion that is connected to a gateelectrode of an amplifier transistor; and the amplifier transistor beingformed on the semiconductor substrate, for amplifying the signal chargetemporarily accumulated in the floating diffusion layer, wherein animpurity concentration of the source/drain diffusion layer of theamplifier transistor is lower than an impurity concentration of thesource/drain diffusion layer of a transistor in the driving unit.
 5. Thesolid-state imaging apparatus according to claim 1, wherein each of thephotosensitive cells includes: a photodiode formed to be exposed on asurface of the semiconductor substrate, for accumulating signal chargeobtained by subjecting, incident light to photoelectric exchange; atransfer transistor formed on the semiconductor substrate, fortransferring the signal charge accumulated in the photodiode; a floatingdiffusion layer formed on the semiconductor substrate, for temporarilyaccumulating the signal charge transferred by the transfer transistor,the floating diffusion layer including a contact portion that isconnected to a gate electrode of an amplifier transistor; the amplifiertransistor being formed on the semiconductor substrate, for amplifyingthe signal charge temporarily accumulated in the floating diffusionlayer; and a reset transistor for resetting the floating diffusionlayer, wherein an impurity concentration of the source/drain diffusionlayer of the reset transistor is lower than an impurity concentration ofthe source/drain diffusion layer of a transistor in the driving unit. 6.The solid-state imaging apparatus according to claim 2, wherein thedriving unit includes: a vertical driver circuit for simultaneouslydriving the transfer transistor and the reset transistor in a verticaldirection; a noise suppressing circuit for obtaining a signal output toa plurality of vertical signal lines disposed in a vertical direction inthe photosensitive region; and a horizontal driver circuit foroutputting a signal from the noise suppressing circuit in a time seriesby successively switching a plurality of horizontal transistors disposedin a horizontal direction, and an impurity concentration of the floatingdiffusion layer is lower than an impurity concentration of asource/drain diffusion layer of a transistor in the vertical drivercircuit.
 7. The solid-state imaging apparatus according to claim 2,wherein the driving unit includes: a vertical driver circuit forsimultaneously driving the transfer transistor and the reset transistorin a vertical direction; a noise suppressing circuit for obtaining asignal output to a plurality of vertical signal lines disposed in avertical direction in the photosensitive region; and a horizontal drivercircuit for outputting a signal from the noise suppressing circuit in atime series by successively switching a plurality of horizontaltransistors disposed in a horizontal direction, and an impurityconcentration of the floating diffusion layer is lower than an impurityconcentration of a source/drain diffusion layer of a transistor in thehorizontal driver circuit.
 8. The solid-state imaging apparatusaccording to claim 2, wherein the driving unit includes: a verticaldriver circuit for simultaneously driving the transfer transistor andthe reset transistor in a vertical direction; a noise suppressingcircuit for obtaining a signal output to a plurality of vertical signallines disposed in a vertical direction in the photosensitive region; anda horizontal driver circuit for outputting a signal from the noisesuppressing circuit in a time series by successively switching aplurality of horizontal transistors disposed in a horizontal direction,and an impurity concentration of the floating diffusion layer is lowerthan an impurity concentration of a source/drain diffusion layer of atransistor in the noise suppressing circuit.
 9. The solid-state imagingapparatus according to claim 6, wherein the vertical driver circuit andthe horizontal driver circuit are composed of a dynamic logic circuit.10. The solid-state imaging apparatus according to claim 6, wherein animpurity concentration of a source/drain diffusion layer of a part of aplurality of transistors constituting the vertical driver circuit andthe horizontal driver circuit is lower than an impurity concentration ofa source/drain diffusion layer of another part of the plurality oftransistors constituting the vertical driver circuit and the horizontaldriver circuit.
 11. The solid-state imaging apparatus according to claim1, wherein the source/drain diffusion layer of a transistor in thedriving unit is covered with a salicide layer.